True rheological instruments (to be distinguished from viscosity indicators) measure flow characteristics related to fluid composition, time dependent behavior, homogeneity, plasticity, yield, viscosity, all generally reduced to a read-out of a shear response as a driven member (usually a spindle) drives another member (usually a cylinder concentric to, and with a close gap relative to, the spindle) via the fluid.
These instruments have been too complex and too expensive to meet the full needs of industrial process users and laboratory users. Also, past designs have not been adaptable to the variety of tests required by users, thereby forcing the purchase of several pieces of equipment, impracticably expensive equipment, or limitations in testing capability.